I like your taste in cars. By any chance, do you have a polarizing filter? Some of the reflections are harsh on the cars and a decent multi-layered circular polarizer might help when screwed on the end of your lens.

I like how you got down nice and low on #3 and #4. #6 is a neat idea and the car looks ready to launch - wouldn't mind seeing the whole car here though..

#3, 4, 5 and 6 are all a little high in terms of exposure.

That nice rx-8 (#5) would look better from a lower angle I think. The picture is also marred a bit by an unflattering background, trash bag, etc..

I like 1 (The sun rays are great) & 2 (the cloud shapes are pretty cool) of your first set, the rest don't do anything for me at all. Very snapshot-ish, the angles don't work.

2nd Set:
First one is highly underexposed.
3. Looks like it was shot with a cell phone, nothing worthy at all imo.
4. Like the idea, but the feet in the mirror next to the car take away from it, and and the car in front of the mirror.
5. The curb, the guy next to it, and the above exhause kill the picture.